Type 1 Diabetes Mellitus (DM) occurs in genetically predisposed individuals as a consequence of immune-mediated destruction of the pancreatic islet insulin secreting beta cells. The onset of the clinical symptoms of diabetes represents the end point of a chronic progressive decline in beta cell function, and it appears only when the majority of beta cells have been lost. Once Type 1 DM develops, individuals require multiple daily injections of insulin to maintain good control and prevent the development of both acute and chronic complications. Good diabetic control is very intensive and often psychologically demanding of an individual. Parenteral insulin has been successfully used to prevent diabetes in animals. In humans, a small study of high risk subjects treated with prophylactic parenteral insulin therapy combining 5 days of insulin by intravenous infusion every 9 months and daily subcutaneous insulin injections showed delay and possible prevention of diabetes. The primary aim in the Diabetes Prevention Trial-Type 1 (DPT-1) is to determine in a multi-center, randomized, trial whether intervention over a six year period with low dose insulin injections in non-diabetic individuals at high risk or an oral insulin to those at intermediate risk to develop Type 1 Diabetes Mellitus can delay or prevent the development of Type 1 Diabetes Mellitus.